The present invention relates to a sewing machine frame made from a synthetic resin in which an arm portion, a tower portion and a bed portion are provided integrally. The present invention also relates to a sewing machine having the sewing machine frame.
In the sewing machine frame, a horizontally extending arm portion supports a reciprocation mechanism for a needle carrying a needle thread, and the tower portion vertically extends from the bed portion for supporting the arm portion in a cantilevered fashion. In the bed portion, a loop taker is supported for trapping a loop of the needle thread carried on the vertically reciprocating needle in order to form a stitch.
In the sewing machine, a smooth stitching operation is required. To this effect, vibration and displacement of a needle tip due to the vertically reciprocating motion of the needle must be reduced or minimized, otherwise a loop seizing beak of the loop taker disposed in the bed portion cannot trap the needle thread loop formed by vertical reciprocation of the sewing needle. Thus, the stitching may be degraded.
In order to avoid this problem, the needle and rotary hook timing must be adequately provided. To this effect, the sewing machine frame must provide high rigidity capable of avoiding deformation or displacement thereof due to reaction force occurring when the needle penetrates a workpice fabric. Therefore, in the conventional sewing machine, a metallic frame having high rigidity is provided in an interior of a sewing machine cover, and a stitch forming mechanism including a needle vertical reciprocating mechanism and the loop taker is attached to the metallic frame.
However, such a conventional arrangement is costly, bulky and heavy. More specifically, the sewing machine frame has a rigid box shape arrangement in order to provide high rigidity. Further, the frame is made from a metal such as a cast iron or aluminum, which in turn increase weight and size. Further, high skill and elaboration is required for assembling the sewing machine because the stitch forming mechanism must be installed into the metallic frame through a small area opening thereof. This increases assembly cost.
Laid open Japanese Patent Application Kokai No.Hei-11-137880 discloses a sewing machine frame made from a synthetic resin to reduce production cost and to provide a light weight frame. As shown in FIG. 16, the frame 300 has an open end arrangement in a U-shape cross-section in which a bed portion 304, a tower portion 303 and an arm portion 302 are provided integrally, and a reinforcing plate 301 is fixed between upper and lower portions at the open end of the bed portion 304.
However, the disclosed sewing machine frame 300 provides a rigidity still lesser than that of the metallic frame. More specifically, as shown in FIG. 16, vertical vibration occurs in the arm portion 302 due to a load exerted along a vertical line containing the needle, the load being caused by the reciprocating motion of the needle during stitching operation. Further, a horizontal swing also occurs at an upper portion of the tower portion 303 during stitching. The horizontal swing may be generated by distortion of the tower portion 303 and the bed portion 304 due to the distortion of the arm portion 302 caused by the vertical reciprocation of the sewing needle.
Accordingly, the disclosed sewing machine frame 300 is still insufficient in terms of rigidity, to lower stitching quality in comparison with the conventional sewing machine provided with the metallic frame.
It is an object of the present invention to overcome the above-described problems and to provide a sewing machine frame having a bed portion, a tower portion and an arm portion those integrally with each other and formed of a synthetic resin, yet having high rigidity, and to provide a sewing machine having such an improved sewing machine frame.
This and other objects of the present invention will be attained by a sewing machine frame for a sewing machine including an integral frame member, and reinforcing ribs. The integral frame member is made from a synthetic resin and provides an outer surface defining an external shape and an inner surface providing an internal space. The integral frame member includes a bed portion, a tower portion upstanding from the bed portion, and an arm portion extending from the tower portion in a cantilevered fashion. The reinforcing ribs are provided at substantially entire area of the inner surface for reinforcing the integral frame member.
In another aspect of the invention, there is provided a sewing machine frame for a sewing machine, the sewing machine including a vertical reciprocation mechanism for a needle carrying a needle thread, and a loop taker trapping a loop of the needle thread carried on the reciprocating needle to form a stitch. The frame includes an integral frame member, and reinforcing ribs. The integral frame member is made from a synthetic resin and provides an outer surface defining an external shape and an inner surface providing an internal space. The integral frame includes a bed portion for supporting the loop taker in the internal space, a tower portion upstanding from the bed portion, and an arm portion extending from the tower portion in a cantilevered fashion for supporting the vertical reciprocation mechanism in the internal space. The reinforcing ribs are provided at substantially entire area of the inner surface.
In still another aspect of the invention, there is provided a sewing machine including a stitch forming mechanism and any one of the above-described sewing machine frame.